I asked this once, and I've researched it. BUT, will the Vltor A5 system be a good choice for my SPR build? 18" mega SPR barrel, rifle gas. Is the buffer that comes in the kit the right weight for this system? Will have a .750 lo-pro block as welll.

Yes

Thank ya sir. Last time I asked there was a lot of ambiguity in the final product, now it's decided.
Now I'm just a few components away and getting excited.

 I switched my 6.8 rifle (16" middy gas) from a rifle-length buffer tube to the Vltor A5 system.  At first it was overgassed, with ejection to about 1:00 oclock.  I had to go to a heavier buffer (6 plus oz) and a Wolfe extra-power rifle spring to bring the bolt speed down and ejection back to about 4:00 oclock.  Extra buffers are sometimes available from Vltor, always available from heavybuffers.com.  Personally, I can't perceive any real advantage to the rather expensive and hard to find A5 components, but then I don't have a GI carbine set up to compare it to. - CW

I use a A5 buffer in a MK 12 the one that comes with the Kit works just fine and is about the same weight as the A2 Standard buffer. The only thing I changed was the buffer spring I went with a rifle Spinco Green spring.